An internally illuminated sign comprising an information display section having at least one flat or curved surface which retroreflects the light coming from the front of the sign and transmits the light coming from the interior of the sign; an illuminator disposed on the back of said display section; and a housing enclosing and holding these information display section and illuminator is known.
For example, Japanese Patent Publication (Laid-open) 1 (1989)-298395-A (U.S. Pat. No. 4,952,023) to Bradshaw, et al. has disclosed:
“an internally illuminated sign comprising an enclosure transmissive to light on at least one side, designated the front side, and cube corner retroreflective sheeting positioned to reflect light incident on the front of the sign, wherein the cube corner retroreflective sheeting:                (1) comprises a cover layer having a multiplicity of retroreflective cube corner members and a base layer of transparent material partially bonded to the cover layer, and        (2) has areas, where the base layer has been bonded to the cover layer, which are:                    (a) optically transparent to internal light with an angle of incidence greater than or equal to zero degrees and less than 90 degrees,            (b) interspersed among the areas occupied by cube corner members, the proportion of such transparent areas to the total sheeting area and their arrangement relative to each other being fixed to allow viewing the sign by means of either internal illumination, retroreflected light, or both.”                        
Japanese Patent Publication (Laid-open) 2 (1990)-285301-A (U.S. Pat. No. 5,122,902) to Benson, et al. also has disclosed:
“an internally illuminated sign comprising a cover transmissive to light on at least one side, designated the front side, a cover to reflect light incident on the front of the sign, and a retroreflective sheet positioned to reflect light incident on the front of the sign, which uses a partially transparent retroreflective article formed by three intersecting sets of parallel grooves, comprising a base, prismatic elements having lateral faces intersecting the base at base edges, and separation surfaces on the base, in which:                (a) each set of grooves has a groove side angle that is constant for that set;        (b) the separation surfaces are transparent, are bounded by the base edges of the lateral faces of the prismatic elements, lie between the prismatic elements in at least one of the grooves and have, taken at any point along any groove in which they lay, curved cross sections.”        
Furthermore, a number of improvements with the view to improve visibility of retroreflective sheetings in the daylight have heretofore been reported, as one of which it is generally known to give a fluorescent appearance to the sheeting by incorporating a fluorescent coloring agent in any one of the layers forming the retroreflective sheeting.
For example, U.S. Pat. No. 3,830,682 to Rowland disclosed that fluorescent retroreflective sheetings of distinct color tone could be prepared by blending a fluorescent coloring agent such as Rhodamine B Extra, Rhodamine 6DGN, Fluorol 7GN or Amaplast Orange LFP with the prismatic layer of triangular-pyramidal cube corner retroreflective sheetings.
U.S. Pat. No. 5,387,458 to Pavelka, et al. has disclosed fluorescent retroreflective sheetings having distinct color tone, comprising a screen layer which is substantially transparent to visible light and absorbs ultraviolet light; and a triangular-pyramidal cube-corner retroreflective element layer to which a thioindigoid, thioxanthene, benzoxazole coumarine or perylene imide dye has been added.
U.S. Pat. No. 5,605,761 to Burns, et al. discloses a fluorescent retroreflective sheeting having distinct color tone, into whose triangular-pyramidal cube-corner retroreflective layer a thioxanthone, perylene imide or thioindigoid fluorescent coloring dye and a hindered amine light stabilizer are added.
Furthermore, U.S. Pat. No. 5,672,643 to Burns, et al. discloses a fluorescent retroreflective sheeting having a color tone within a specific range, in which the reflective element layer in a cube-corner retroreflective sheeting contains, in combination, a perylene imide fluorescent coloring agent having a specific structure and a specific fluorescent coloring agent among Lumogen F Yellow 083, CI Solvent Yellow 160:1, CI Solvent Green 4, CI Pigment Yellow 101, CI Solvent Yellow 131, CI Solvent Yellow 98, Oraset Yellow 8GF, CI Solvent Green 5 and Golden Yellow D-304.
Said cube-corner retroreflective sheeting (corresponding to the prismatic retroreflective sheeting said in the preset invention) shown in the Bradshow Patent, however, comprises a cover layer having a multiplicity of retroreflective cube-corner members and a base layer of transparent material bonded to the cover layer and, because the base layer has the areas bonded to the cover layer, at the bonded areas the retroreflective function of the prismatic retroreflective elements is destroyed. The sheeting, therefore, is subject to a problem that its retroreflectivity as a whole is markedly reduced.
Retroreflective sheetings having such bonded areas are heretofore well known and are normally marketed as retroreflective sheetings of a form as disclosed in U.S. Pat. No. 4,025,159 to McGrath, for example, to secure an encapsulation structure to insure provision of an air layer behind the prismatic retroreflective elements. Said patent also discloses various resins capable of forming optically transparent or non-transparent bonded areas, to give an encapsulation structure to glass beads retroreflective sheeting or cube-corner retroreflective sheeting.
These prismatic retroreflective sheetings as described in the above are well known, for example, as Scotchlite Diamond Grade manufactured by Minnesota Mining and Manufacturing Company, U.S.A., or Nikkalite Crystal Grade manufactured by Nippon Carbide Industries, Co., Inc. According to measurements conducted by the present inventors, the reduction in retroreflectivity of these products due to their encapsulation structure amounts to as much as 30 to 40%. It was also found that percent transmission of light from an illuminator placed at the back decreases at the bonded areas.
The products furthermore are subject to problems that their appearances are impaired or relatively small-sized letters displayed thereon are difficult of reading, because a uniform appearance cannot be achieved with above encapsulation structures wherein the retroreflective areas and sealing bond areas differ in color and qualitative impression.
Also in such retroreflective sheeting as proposed by Benson, which uses prismatic retroreflective elements having separation surfaces therebetween, the prismatic retroreflective elements are absent at the areas where the separation surfaces are provided, similarly to the elements disclosed in Bradshaw, and hence the sheeting is subject to a problem that its reflectivity as a whole is markedly reduced.
In an internally illuminated sign, its light source is installed inside said sign and a drawback of reduced visibility hardly arises no matter from which direction the sign is viewed. In occasions of power failure or lamp trouble, however, presence of the sign is confirmable only by retroreflection of the light from its head lamp. In such occasions, in particular, when the light's incident or entrance angle is large, visibility of the sign is drastically impaired. Hence it is particularly important for internally illuminated signs to use retroreflective elements of excellent entrance angularity. Internally illuminated signs using retroreflective elements exhibiting such excellent entrance angularity, however, are heretofore unknown. Moreover, internally illuminated signs known heretofore are subject to still additional problem of entrance angularity degradation, simultaneously with the reflectivity reduction caused for the reasons as describes in the above.
On the other hand, for many of the traffic signs equipped with commercialized prismatic retroreflective sheetings, fluorescent colors are adoped for excellent visibility in the daytime. It can be easily inferred to adopt such fluorescent-colored prismatic retroreflective elements to those internally illuminated signs as shown in the patents to Bradshaw or Benson. Whereas, while adoption of fluorescent colors may improve the sign's daytime visibility, it is still difficult to solve the problem of reduction in retroreflectivity or to achieve excellent angularity.
Accordingly, therefore, an object of the present invention is to provide an internally illuminated sign which can be used for traffic signs such as road signs, regulatory signs, guide signs and construction signs, and commercial signs, and which exhibits improved visibility not only in daytime but also at night, because it is equipped with an information display section having a surface which retroreflects light coming from the front of the sign and transmits light from interior of the sign.
Another object of the present invention is to provide an internally illuminated sign having excellent visibility at wide angle range even in occasions of power failure or lamp trouble, because of its adoption of retroreflective elements which exhibit excellent retroreflective characteristics at broad entrance angle range.
A still further object of the present invention is to provide an internally illuminated sign in which the color used in the information display section in said retroreflective, internally illuminated sign is fluorescent in daytime, and visibility of the sign not only in daylight but at night is further improved.